The Heidelberg cohort of the European Prospective Investigation into Cancer and Nutrition (EPIC-Heidelberg) (n=23,943) did not find a statistically significant effect of vitamin/mineral supplementation on cancer risk (beneficial or harmful). It did find baseline users of antioxidant supplements had a 48% reduced risk of cancer mortality. Because of a ‘sick-user effect’, researchers are advised to be cautious that bias isn’t introduced with the conversion of 'sick' non-users to users-of-supplements during research studies.

Scientists are expected to be diligent. When conducting vitamin/mineral supplementation studies, it is reasonable to criticize reports that rely upon randomization (supplement vs placebo) without consideration of vitamin status, e.g. serum α-tocopherol concentrations, of the volunteers.